This invention relates to a method and apparatus for cleaning the ends of pipes or tubes in preparation for welding. Before aluminum and certain other metals can be welded, the surface to be welded must be properly prepared and cleaned. Cleaning may be accomplished either mechanically, chemically or electrically. Of these three processes, electrical cleaning is preferred in many instances because it is a simple, inexpensive and highly effective process. In addition, it appears that an electrically cleaned surface will remain in a condition for welding for a much longer period of time than a chemically cleaned or etched surface.
Electrically cleaning a surface usually involves the use of a non-consumable electrode, such as a tungsten electrode, wherein the electrode is made positive relative to the workpiece. In some cases, a separate cleaning electrode is used prior to the welding operation. In other cases, particularly where the surface to be welded is substantially clean, alternating current may be applied to a welding electrode, and the surface cleaned sufficiently during the reverse polarity portion of the alternating current cycle during the welding process. In either case, an inert gas is provided to protect the heated surface from further oxidation during the cleaning and/or welding process.
When joining aluminum pipes, it is essential that not only the root face but both the inner and outer surfaces of the pipe be adequately cleaned prior to welding, and this has been traditionally accomplished by cleaning the ends of the pipe chemically. However, as pointed out above, a chemically cleaned surface will usually not remain clean indefinitely, and where there are many pipes to be welded, it is not always possible to perform the welding operation soon enough after cleaning and therefore the resultant weld frequently reveals embedded defects.
Thus, there is a need to provide a method and apparatus for effectively cleaning the ends of aluminum tubing or pipes prior to welding, preferably electrically cleaned pipes so that defect-free joints will result even though a substantial amount of time has elapsed between the cleaning and the welding operations.